textproduct: Albany

WHAT HAS CHANGED

No significant changes. Minor adjustments to temperatures, wind gusts, POPs, and snowfall amounts tonight through Friday. Confidence in a significant cold weather outbreak remain moderate to high Friday night through Sunday night.

KEY MESSAGES

1) Snow showers and a few snow squalls, mainly west of the Hudson River Valley, expected this evening along with gusty winds as an arctic cold front sweeps through the region.

2) Colder than normal temperatures likely tonight through Wednesday with heavy lake effect snow accumulations for the western Adirondacks tonight through Tuesday night resulting in difficult travel. Additional snow accumulations likely for areas mainly near and north of I-90 Wednesday into Friday.

3) Moderate to high confidence for dangerous cold temperatures Friday night through Sunday night. Extreme Cold Weather Warnings and Cold Weather Advisories will likely be needed.

DISCUSSION

KEY MESSAGE 1...

Our next Arctic cold front continues to march eastward through Ontario and the Ohio Valley this afternoon with snow showers and snow squalls already underway across western PA and western NY. Southwest winds have turned breezy this afternoon ahead of this boundary with gusts up to 25-35 mph expected through this evening with lapse rates steepening to 7-8C/km as the front approaches. Latest guidance shows the low-level thermal and moisture gradient associated with the boundary tracking into the Mohawk Valley by 22 - 00 UTC which represents the most likely timing of the snow showers/snow squalls. The boundary then tracks into the eastern Catskills and the Capital District towards 00 - 02 UTC before finally into western New England by 02 - 04 UTC. Snow squall parameter values increase as the front moves into areas mainly west of the Hudson River this evening suggesting that favorable parameters for snow squalls are in place; however, values decrease noticeably as the front shifts east indicating that the snow squall potential decreases after 03 UTC.

During any snow squalls or heavy snow showers this evening, brief reductions to visibility are possible between gusty winds and burst of moderate/heavy snow leading to a quick coating to 0.5" of light/fluffy snow. Most snow showers should exit into New England by Midnight, ending the snow shower/squall potential.

KEY MESSAGE 2...

Westerly flow will usher a much colder air mass into the Northeast tonight in the wake of our arctic front with the cold air advection regime supporting deep mixing and breezy winds gusting to 25 - 35mph overnight. With 850 hPa isotherms dropping to -18C to -22C by 12 UTC Tues, expecting Tuesday morning lows to fall into the single digits and low teens across eastern NY and western New England. There is about a 40 to 50% chance for Tues A.M temperatures to fall to 10F or lower in the Hudson Valley from Poughkeepsie to Albany while the chance is greater than 60% across the rest of the region. The combination of such cold temperatures and continued breezy winds will support chilly "feel-like" temperatures ranging from 5F to -5F with the higher terrain areas in the southern Greens and southern Adirondacks ranging -10F to -15F. Not quite cold enough to warrant a cold weather advisory but worth mentioning as such cold temperatures occur during the Tues A.M commute after the holiday weekend.

As such cold temperatures infiltrate the region tonight, the W-SW cyclonic flow will become well aligned across the long fetch of Lake Ontario generating a rather impressive lake effect snow band. The difference between the Lake Ontario waters (~3-4C) and the incoming air mass ranks within the Extreme lake induced instability class and while the band will initially be directed to our north into the North Country, as the winds veer to the west by 03 - 06 UTC, the band will drop into Herkimer and Hamilton County but remain near/north of Route 28. The instability values will easily support high snowfall rates with the HREF showing high probabilities for 1"+ per hour snowfall rates overnight tonight; however, as was mentioned in the previous discussion, the inland extent of these high snowfall rates may be less than usual due to the high instability. So while there remains high confidence in the heavy snowfall rates reaching N. Herkimer County, confidence decreases farther east into Hamilton County. The band looks to weaken a bit by 12 - 18 UTC Tuesday as brief subsidence builds overhead but the band then reinvigorates by Tuesday afternoon with snowfall rates intensifying back towards 1"+ per hour into Tuesday evening (although rates may not be as high as Mon night per the latest HREF probability values) before weakening and lifting northward again by/shortly after Midnight as the low and mid-level flow backs to the southwest. Our current winter storm warnings/advisories continue through 12 UTC Wed but these may end earlier as the bands weakens.

Overall snowfall totals continue to range 6 to 10" for northern Herkimer County (locally 10 to 12") with 3 to 6" in northwest Hamilton County. Given that the intensity of the band varies with the band oscillating at times through Tuesday night, snowfall amounts near 12" should be rather isolated and limited to areas where the heavy snowfall rates can persist the longest.

After a brief break from the lake effect Wednesday morning, yet another clipper looks to support isentropic lift Wednesday afternoon into Thursday morning mainly along the south facing slopes of the southwest Adirondacks into the Upper Hudson Valley and southern Greens into Wed night. This will support additional light to moderate snow accumulations mainly for areas along and north of I-90 before the main cold front approaches during the day on Thursday leading to additional snow showers.

KEY MESSAGE 3...

Moderate to high confidence for a period of dangerously cold temperature Friday night through Sunday night across eastern NY and western New England. After an Arctic cold front pushes across the region on Friday, there remains strong agreement among the deterministic and ensembles guidance that the coldest air of the season surges into the Northeast through the weekend. In fact, when examining the extreme forecast index (EFI) to learn just how unusual these temperature values are, we see values ranging between -0.8 and -0.9. This is impressive and indeed suggests this event is unusual, even for late January standards when we typically experience the coldest temperatures of the year.

While the exact magnitude of the cold may fluctuate since this event is still several days away, the latest NBM probabilistic values show 30-70% chance for overnight low temperatures to fall under 0 degrees in valley areas Fri night and Sat night with a 50 to 75% chance for overnight lows to fall under -10F in the southwest Adirondacks and southern Greens both nights. With a continued northwest breeze also in place Friday night, wind chill values may certainly become dangerous and we have low to moderate confidence that Extreme Cold Watches/Warnings may need to be issued for the high terrain with moderate to high confidence in needing cold weather advisories for most lower elevation areas.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Through 00Z/Wed, scattered snow showers will be possible through 01Z-02Z/Tue at KGFL, KALB and KPSF with brief MVFR/IFR Vsbys possible. Otherwise, VFR conditions are expected through the period, with intervals of Cigs of 5000-7000 FT AGL possible Tuesday afternoon at KGFL, KALB and KPSF. A few flurries will also be possible at KPSF Tuesday afternoon. Winds will be southwest to west and increase to 8-14 KT tonight with some gusts up to 20-25 KT possible. West winds will continue at 10-15 KT Tuesday with gusts of 25-30 KT possible, strongest at KALB and KPSF. Low level wind shear is possible prior to the increasing winds this evening at KGFL and KPOU, as lighter surface winds of less than 10 KT occur while winds around 2000 FT AGL increase from the southwest/west to 30-35 KT.

Outlook...

Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Low Operational Impact. Slight Chance of SN. Wednesday Night: Low Operational Impact. Breezy. Slight Chance of SN. Thursday: Low Operational Impact. Chance of SHSN. Thursday Night: No Operational Impact. NO SIG WX. Friday: Low Operational Impact. Breezy. NO SIG WX. Friday Night: No Operational Impact. NO SIG WX. Saturday: No Operational Impact. NO SIG WX.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...Winter Storm Warning until 7 AM EST Wednesday for NYZ032. Winter Weather Advisory until 7 AM EST Wednesday for NYZ033. MA...None. VT...None.